Charles Komanoff's excellent work on carbon taxes vs. emission trading tends to attract certain frequent objections. This is an attempt to answer some of them:
Cap and trade is the way we do things now. Politically, we can never win a carbon tax.
Answer: Cap and trade has political heft mainly because it was instituted at a low level over a long period of time -- thus it did not require very high emission reductions. Further, because the emission cap was confined to a few nations, but emission credits can be bought from nations without such caps, the emission reduction as a percent of total emissions in countries taking part in the Kyoto negotiations is even lower than the nominal target.
In addition, emission reductions are measured against a 1990 baseline, which has been increased by 3% due to various revisions (subscription). And while there is room for argument over just how many, there is no question that a fair percentage of Kyoto credits are fraudulent -- excessive credits were granted to EU utilities, and many of the CDM credits sold in China are bogus.
Put a tight enough cap on the number of credits, with stricter controls to prevent fraud, and you will find political resistance is as great as resistance to a carbon tax.